This is my homemade air cannon, made to shoot anything that will fit inside the barrels. It has a 5lb fire extinguisher as the air tank, a 3/4” brass ball valve with a spring loaded action, and can use any barrel size that fits the 1/2” male threading. I am currently running it at 80-100 PSI with great results and looking to move up (slowly) to 300 PSI. The valve is easy to make, simple, and can open very quickly (if you do it right, haven’t quite got that down yet). I have barrels in 3/4”, 1 1/2”, 2”, and 3” so be assured it’ll shoot anything you want lmao. Receiver is made from Plexiglas, as well as some main components.

Anyhow, a bit of background on this. I’ve never really liked airguns and air powered designs. When I was first starting to make stuff I tried to make air guns but since I was flying into them completely blind and being too stubborn to read up on how compressed air works, they failed to work for me. It seemed that no matter what I would do, the Schrader valve would just spray out air. That sorrowful piss-like noise ended my interest in air power LOL. Regardless, my taste for pneumatic things has been sour and I’ve stuck to mechanical designs such as crossbows or spring guns.

But my 18th birthday is coming up, and I was wanting to have fun just blowing stuff up with my friends (less juvenile more hillbilly). I wasn’t quite sure if I could make something powerful enough. I considered a ballista, but it would prohibited to round shot or long bolts, with little leeway for other projectiles. Would also be prohibitively large if I wanted it to be safe yet powerful and simple. I then looked at a giant slingshot, but that would be even more limited to round shot only. It would also be very large and would require a complex winch system to cock it and all that. Overall I couldn’t really think of anything simple and easy yet powerful enough to blow some stuff up.

And while I was scavenging for a winch (never found the right one), I also found an old empty fire extinguisher, and that really changed my mind haha. Tapped the threads and rigged it to a ball valve and I was instantly a believer in pneumatic power I found that a fire extinguisher and a ball valve at 100 PSI would toss a 3lb steel spike with the same force as a #400 ballista, with far less complexity, cost, or possible deadly failure. So yeah, I’m definitely a believer in airguns now, and for the past month I’ve been extremely obsessed haha getting a little unhealthy, I won’t lie.

But yeah long stories aside, I wanted something that could launch anything I want with great power. With proper wadding and loading this cannon manages to launch anything from birdshot all the way up to full size shovels, sledge hammer heads, and spears too. The heavier stuff is going very slow but much faster than most homemade ballistas ever would, and the lighter stuff is exceeding the velocities of everything else I’ve made, so I say it’s a win-win. I’ve also made a spear-launching barrel for it based on a spigot mortar, which is very neat.

It’s rather annoying to pump up every shot but I don’t think it’s very feasible to make a repeating air cannon unless you’ve got a scuba tank as your tank or something overly expensive and dangerous. I know CO2 works but I’m too cheap. Unless I’m wrong and it is possible, but who knows.

But yeah, turns out air guns are way cooler than I thought. Expect a lot of silly questions from me and my rambling mind LOL, hopefully some build posts too.

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I loved the shovel shot, ever since hearing that the Spetsnaz sharpened their shovels to use as throwing weapons I've wanted to build an entrenching tool launcher...

My one criticism is that you're standing a little too close for some ammunition that rebounds, safety glasses won't necessarily be enough if a hammer head comes hurtling back at your head.

I found that a fire extinguisher and a ball valve at 100 PSI would toss a 3lb steel spike with the same force as a #400 ballista, with far less complexity, cost, or possible deadly failure.

Once you go pneumatic you rarely go back - same story with spring powered airguns vs PCPs, no comparison as you move to higher power.

It’s rather annoying to pump up every shot but I don’t think it’s very feasible to make a repeating air cannon unless you’ve got a scuba tank as your tank or something overly expensive and dangerous.

Consider a smaller chamber at higher pressure, a 4500 psi stirrup pump can be obtained fairly cheaply and you will see better performance. A 1 liter bottle at 100 psi and a 0.5 liter bottle at 200 psi is technically the same amount of air, but the latter has a greater power potential. Here is a little GGDT comparison:

All factors are equal except that in the second example, I halved the chamber volume and doubled the pressure.

Muzzle energy jumped from 222 ft lbs to 331 ft lbs, an increase of almost 50%.

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hectmarr wrote:You have to make many weapons, because this field is long and short life

Thank you so much for the helpful info JSR, exactly what I was looking for. Also yeah, I moved back a lot more in the later shots but it was hard to capture the projectile flight from afar. I avoided a lot by simply angling myself from the target so that it would glance off to the left or right. Either way yeah I gotta either get more of an angle or stand farther back.

A short word on shovel launchers (LOL) make sure you have a flat blade! The shape of the blade causes some very haywire trajectories at longer ranges and it’s very unpredictable. If I were to design one I’d use one of those tacticool telescoping shovels and adapt it to a spigot mortar design, like my spear launching barrel.

And what you’ve said to me is pretty much exactly what I was wanting to know. I went with high volume and low pressure but I’m definitely wanting to love to high pressure low volume. It’s just rather nerve wracking and I don’t know high a pressure I should take these fittings. I got some questions for you then:

-do you know of an easily-sourced cheap 300 PSI capable air tank with a 3/4” female end? I’ve only found fire extinguishers to work for this. Something of a smaller size with little airflow restriction would be a blessing from above.

-I’ve also considered making a stirrup pump myself, since the cheapest ones here are like $80.00 and I’m still quite cheap. Should I make one or should I buy the $80 one?

-and this ones kind of unrelated but I was wondering your opinion on a multi shot launcher. I’ve made some little designs for a hammer valve system but I’m not sure if enough air can be stored and released repetitively with such a large bore. I feel like you can’t get much more than a single shot unless you try CO2. Perhaps it’s possible? I don’t know.

do you know of an easily-sourced cheap 300 PSI capable air tank with a 3/4” female end?

Why not make your own using 3/4" or 1" steel pipe nipples?

I’ve also considered making a stirrup pump myself, since the cheapest ones here are like $80.00 and I’m still quite cheap. Should I make one or should I buy the $80 one?

If you're cheap there are ways to make your own but honestly, $80 is not much to shell out for a reliable 4500 psi multi-stage pump.

I was wondering your opinion on a multi shot launcher. I’ve made some little designs for a hammer valve system but I’m not sure if enough air can be stored and released repetitively with such a large bore. I feel like you can’t get much more than a single shot unless you try CO2.

A big bore multishot is certainly a possibility, however rather than a direct hammer valve I would go for a hammer valve pilot to momentarily open an exhaust valve:

The problem you'll run into is generating enough air. Throwing some numbers out there, say you wanted to make a 1" bore multishot, with a 1" diameter, 12" long air chamber at 300 psi, fed by a 48 ci paintball tank regged down from 3000 psi.

Assuming the approx 9 ci chamber was closed off, pressure drops to 50% after the first shot and we get a useful velocity of 251 feet per second with a 1" steel ball. A 48 ci paintball tank regged down is however giving us an additional volume of 480 ci of air at 300 psi, that's going to give us enough air for 45+ full power shots.

Now, can a 48 ci paintball tank be filled with a stirrup pump? Yes, it's possible. The question is, once you've done it once, will you be willing to do it a second time? At that point, some sort of powered assistance is going to be desirable.

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hectmarr wrote:You have to make many weapons, because this field is long and short life

Huh, I see. That’s sort of what I was expecting. My other idea was a a cannon with a built in underlever pump. I feel like that would be a lot more useful and portable, most of all probably easier to pump. As for an air tank, I have a smaller fire extinguisher laying around so I’ll probably use that. Unless I should go smaller than that? Do you have a sort of general measurement for the tank I should use? I honestly don’t know, I’m not a measurement guy.

The main thing with getting such a high pressure pump is that I’m worried I’ll get too tempted to push the limits of my air tanks since the tank is supposed to go to such a high pressure. I’d rather have a 300-600 PSI pump since I don’t have any materials that can withstand more than that. But meh, I’ll probably end up buying a stirrup pump.

Sorry for such a wave of questions but I’m new to this and I don’t want to blow up haha

jacoblesann wrote:Huh, I see. That’s sort of what I was expecting. My other idea was a a cannon with a built in underlever pump. I feel like that would be a lot more useful and portable, most of all probably easier to pump. As for an air tank, I have a smaller fire extinguisher laying around so I’ll probably use that. Unless I should go smaller than that? Do you have a sort of general measurement for the tank I should use? I honestly don’t know, I’m not a measurement guy.

I strongly suggest GGDT, D_Hall's website is down but here is the file hosted temporarily. I know the feeling of not being a "measurement guy" but virtually modeling your launchers beforehand saves you a lot of failed prototypes.

The main thing with getting such a high pressure pump is that I’m worried I’ll get too tempted to push the limits of my air tanks since the tank is supposed to go to such a high pressure. I’d rather have a 300-600 PSI pump since I don’t have any materials that can withstand more than that. But meh, I’ll probably end up buying a stirrup pump.

You could always add a pop-off valve that physically prevents you from going any higher than a certain pressure.

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hectmarr wrote:You have to make many weapons, because this field is long and short life

Huh, I suppose that’s true too. My plan right now is to make my own pump for my upcoming birthday so we can have some fun blowing stuff up , and then once I get enough money sometime I’ll get the $80 pump. I’ve also bought some adapter to change my fire extinguisher from a 5lb to one of those smaller ones. 3lbs? Idk but it makes a far better stock.